Servo mechanism



June 2 1964 D. P. scoTTo E'rAl. 3,135,164

SERV() MECHAN ISM INIENTORS. DOMINICK'P. SCOTTO DANBIlt/ZL. J.

Sid

W LA? A TTOPNC Y United States Patent O 3,135,164 SERV() MECHANISM Dominick P. Scotto, Nassau, N.Y., and Daniel I. Mager, Brevard County, Fla., assignors to American Bosch Arma Corporation, a corporation of New York Filed Nov. 16, 1959, Ser. No. 853,255 4 Claims. (Cl. 91-47) The present invention relates to hydraulic servos and has particular reference to long-displacement, linear-motion devices, such as control rod actuators.

Control rod actuators for atomic reactors are utilized for driving the control rod to, and holding it at, a specified position in the atomic pile. Linear hydraulic servos for this purpose have been proposed before, but the present invention eliminates many of the manufacturing problems and operating deficiencies of prior devices of this type.

In the basic and prior devices, the position of a piston, attached to the control rod, in a cylinder is controlled by the fluid flow to both sides of the piston, the llow to the two ends of the cylinder are controlled by the position of an orifice opposite a longitudinal slot through the cylinder wall in which a key on the piston slides. Since the pressure on the side with greater flow is less than on the other side, the piston moves toward the orice until the piston key covers the orifice so as to equalize the fluid flow out of each cylinder end. Thus, the piston is centered over the orifice and the position of the orice controls the position of the piston and control rod. The orifice position is controlled by rotating an outer cylinder, having a helical slot through its wall, with respect to the inner cylinder, having the longitudinal slot therein. The intersection of the two slots provides the orilice for the lluid while the longitudinal position of the intersection is controlled by the rotational displacement of the outer cylinder.

In a principal embodiment of the present invention, the cylinder is fed with high pressure lluid to one side of the piston only, a compression spring on the opposite side providing the opposing force to the piston movement. The pipe leading the iiuid to the cylinder extends along the inner wall of the cylinder to provide a key for preventing rotation of the piston. This key allows the oriice to be produced by a pair of helically arranged openings in the walls of the piston cylinder as well as in the outer rotatable cylinder. The openings are preferably made to be porous, but not completely unrestrictive to llow, in the interest of rigidity and strength. For example, the opening may comprise a host of small diameter holes covering the area designated for the helical opening. For additional strength, the openings are not arrayed in a continuous slot, but are arrayed over the cylinder walls in proper relationship to provide an orifice at the appropriate longitudinal position upon rotation of the outer cylinder.

The extended displacement required of the rod necessitates a long inner cylinder. The outer cylinder, to be closely litted to the inner cylinder, is made iiexible so as to reduce the manufacturing tolerances required of the inner cylinder.

The position of the piston is indicated by the rotation of a central shaft produced by a key on the piston engaging a helical slot in the central shaft.

For a more complete understanding of this invention, reference may be had to the accompanying diagrams, in which:

FIG. l shows a cross section of the improved valve;

FIG. 2 shows the relationship between helical slots of the valve cylinder;

FIG. 3 shows a detail of the outer cylinder construction;

3,135,164 Patented June 2, 1964 FIG. 4 shows a possible noncontinuous arrangement of openings for the cylinders;

FIG. 5 is a detail section of a small portion of the flexible cylinder;

FIG. 6 is a section through 6-6 of FIG. 5; and

FIG. 7 is a sectional view through line 7-7 of FIG. 1.

With reference now to FIG. l of the drawings, a piston 10 is attached to a hollow shaft 11 and is arranged to travel vertically in a cylinder 12. A pipe 13 is attached to the inner wall of the cylinder 12 and serves to connect a source 14 of pressurized fluid to the lower portion of the cylinder 12. The pipe 13 also serves as a key which lits into a recess 10a in the piston 10 as seen more clearly in FIG. 7 to prevent rotation thereof, for purposes to be described later. The end of pipe 13 leads into a depression 15 in the end of cylinder 12 through which the lluid is allowed to reach the bottom of cylinder 12.

On the wall of the cylinder 12 is a porous band 16 preferably arrayed in a helical manner, as shown partially in FIG. 2, and represented by the opening 16 in the cylinder 12 of FIG. l. Closely surrounding the cylinder 12 is an outer cylinder 17 which also has a porous helical slot 18 cut therein, the helix 18 preferably advancing oppositely to the helix 16, asin FIG. 2,' although not necessarily so.

The outer cylinder 17 is comprised of a quantity of rings 17a, 17b, 17C, etc. stacked on one another and held together with spring-like bands 19, FIG. 3. The edges of band 19 fit into grooves on the rings` and the band 19 completely encircles the rings, except for the space provided for the porous section 18. FIG. 3 shows the porous helix 18 as being particularly composed of a band of small holes, while FIG. 2 schematically illustrates the helix as a mesh construction of some sort, but generally represents any type porous section.

In order to prevent relative rotation of the rings 1717, 17C, etc., pins 20 connect each of the rings to the spring 19. The pins 20 do not restrict translation motion between the rings and, therefore, permit the stack of rings to follow the contour of the inner cylinder 12.

In the device in FIG. l, the outer cylinder 17 is normally positioned, prior to actual operation, so that the opening at the intersection of helices 16 and 18 is at the bottom of the cylinder 12 and no pressure can build up in the lower part of the cylinder. lin order to control the position of shaft or rod 11, the outer cylinder 17 is rotated to cause the intersection of the helices to move upward opposite the desired position of the piston 10.

Since the intersection is above the piston 10, the pressure of fluid from pump 14 builds up under the piston 10 and forces the piston upwards, against the action of the spring 21 which is located between the top 22 of cylinder 12 and the piston 10. As the piston 10 moves across the orifice produced at the intersection of helices 16 and 18, the leakage of lluid out of cylinder 12 increases until the size of the hole uncovered is just sufficient to produce that leakage which will balance the fluid pressure below the piston 10 against the spring pressure above the piston 10. It will be understood that in the position of the apparatus shown in the figures the weight of rod 11 and parts attached thereto acts in the same direction as spring 21, and when this weight is large enough it may be used without the aid of spring 21 to move the piston downwardly. The piston 10 and rod 11, therefore, come to rest at the desired position dictated by the rotational displacement of outer cylinder 17. The uid which leaks out of cylinder 12 is collected in chamber 40 and returned to pump 14 by piping 41.

If the cylinder 17 is now rotated to put the intersection below the piston, the leakage out of the orifice will be so great that the pressure drops in the lower part of the cylinder and the spring 21 drives the piston 10 downward until just the right amount of the orifice is covered to maintain the pressure below the piston 10 and to hold the piston at the desired position.

In the event of emergency, it is imperative to push the rod 11 all the way out of cylinder 12 as quicklyas possible. In this event, the clutch 23 between motor 24 and the gearing 25 which drives the cylinder 17, is deenergized and the cylinder 17 is rotated back to its normal position as the spring 26, which is attached to the top of the cylinder 17 and to the flange at the bottom of cylinder 12, unwinds. Thus, the orifice is moved to the bottom of the cylinder 12 and the spring 21 drives the piston and rod 11 downwards.

Shock is minimized by the provision of a ring 27 on piston 10 which fits into a groove 28 on the bottom of cylinder 12. As the piston approaches the bottom of the cylinder, the forcing of the fluid out of the groove 28 by the ring 27 cushions the downward motion of the piston and brings it to a smooth stop.

The longitudinal position of the piston 10 is indicated on a drum indicator 29, opposite the index 30, by providing a shaft 31, concentrically of and telescoped within rod 11 with a helical groove 32. A key 33 on piston 10 fits into the groove 32 and, since the piston is prevented from rotation by the pipe 13, the shaft 31 is rotated, and its rotational position is a measure of the longitudinal position of the piston 10. A thrust bearing 32 in plate 22 permits rotation of shaft 31 but prohibits longitudinal motion thereof. Furthermore, the bearing 34 is preferably sealed to prevent leakage of any fluid through the bearing 32, even though the amount of fluid above the piston usually will be small.

For automatic positioning of the rod, a desired positional signal at 3S is compared with an actual positional signal from potentiometer 36, which is positioned according to indicator 29 by gearing 37 and the error signal at 38 energizes motor 24 which drives gearing 25 through clutch 23. When the actual position of shaft 11 matches the desired position, the motor 24 is deenergized and the rod is correctly positioned.

FIG. 4 shows an array of openings which act like the continuous slots but present a more rigid device. The mating surfaces of cylinders 12 and 17 are developed in FIG. 4 with the cross-hatched areas representing porous areas on one cylinder and the dotted quadrangles representing porous areas on the other cylinder. On any horizontal line the spacing between the cross-hatched and dotted rectangles is equal to the distance between the two diagonal dotted lines which represent the positions which would be occupied by the continuous helices 16 and 18 on each of the cylinders 12 and 17. It should be recognized that the arrangementof FIG. 4 is merely illustrative and many other designs can be made following the explanation above.

FIGS. and 6 show an alternative construction of the cylindrical segments 17a, 17b where the mating surfaces between adjacent segments are spherical instead of fiat, as shown in FIG. 3. The radius of the sphere defining the surface is on the order of the diameter of the cylinder 17, but is by no means limited to that value. To prevent relative rotation between the cylinder segments, a pin 39 on one cylindrical segment 17a projects into a socket 40 on segment 17b. The socket 40 is designed to permit rotation between the segments about an axis substantially perpendicular to the axis of the cylinder 17, but to prevent rotation about an axis parallel thereto. A number of pins and sockets 39, 40 are equally spaced about the circumference of the cylindrical sections. Thus, the construction of FIGS. 5 and 6 permits rotation of the segments, whereas the construction of FIG. 3 permits translations of the segments with respect to the adjacent segment.

We claim:

1. In a device of the character described, a sleeve, a cylinder mounted within said sleeve, said sleeve and cylinder being mounted for relative rotational movement, means for rotating said sleeve with respect to said cylinder, a piston within said cylinder, means for applying fluid pressure on one side of said piston, means applying pressure on said piston opposing said fluid pressure, said sleeve and said cylinder each having intersecting passageways whereby rotation of said sleeve Will effect longitudinal motion of said piston to the position where the passageways intersect, torsional spring means connected to said sleeve and to said cylinder and adapted to be stressed upon rotation of said sleeve, said torsional spring means returning said sleeve to a predetermined position upon deactivation of said rotating means.

2. In a device of the character described, a sleeve, a cylinder mounted within said sleeve, said sleeve and cylinder being mounted for relative rotational movement, means for rotating said sleeve with respect to said cylinder, a piston within said cylinder, means for applying uid pressure on one side of said piston, means applying pressure on said piston opposing said uid pressure, said sleeve and said cylinder each having intersecting passageways whereby rotation of said sleeve will effect longitudinal motion of said piston to the position where the passageways intersect and a liquid passage internally of said cylinder and forming a key for said piston to prevent rotation thereof, torsional spring means connected to said sleeve and to said cylinder and adapted to be stressed upon rotation of said sleeve, said torsional spring means returning said sleeve to a predetermined position upon deactivation of said rotating means.

3. In a device of the character described, a sleeve, a cylinder mounted within said sleeve, said sleeve and cylinder being mounted for relative rotational movement, means for rotating said sleeve with respect to said cylinder, a piston within said cylinder, means for applying uid pressure on one side of said piston, resilient means applying pressure on said piston opposing said fluid pressure, said sleeve and said cylinder each having intersecting opposed helical passageways whereby rotation of said sleeve will effect longitudinal motion of said piston to the position Where the passageways intersect, torsional spring means connected to said sleeve and to said cylinder and adapted to be stressed upon rotation of said sleeve, said torsional spring means returning said sleeve to a predetermined position upon deactivation of said rotating means.

4. In a device of the character described, a sleeve, a cylinder mounted within said sleeve, said sleeve and cylinder being mounted for relative rotational movement, means for rotating said sleeve with respect to said cylinder, a piston within said cylinder, means for applying uid pressure on one side of said piston, means applying pressure on said piston opposing said fluid pressure, said sleeve and said cylinder each having intersecting opposed helical passageways whereby rotation of said sleeve will effect longitudinal motion of said piston to the position where ythe passageways intersect and a liquid passage internally of said cylinder and forming a key for said piston to prevent rotation thereof, torsional spring means connected to said sleeve and to said cylinder and adapted to be stressed upon rotation of said sleeve, said torsional spring means returning said sleeve to a predetermined position upon deactivation of said rotating means.

References Cited in the file of this patent UNITED STATES PATENTS 2,187,513 Evans -.,--H--E-E- l-n Ian. 16, 1940 

1. IN A DEVICE OF THE CHARACTER DESCRIBED, A SLEEVE, A CYLINDER MOUNTED WITHIN SAID SLEEVE, SAID SLEEVE AND CYLINDER BEING MOUNTED FOR RELATIVE ROTATIONAL MOVEMENT, MEANS FOR ROTATING SAID SLEEVE WITH RESPECT TO SAID CYLINDER, A PISTON WITHIN SAID CYLINDER, MEANS FOR APPLYING FLUID PRESSURE ON ONE SIDE OF SAID PISTON, MEANS APPLYING PRESSURE ON SAID PISTON OPPOSING SAID FLUID PRESSURE, SAID SLEEVE AND SAID CYLINDER EACH HAVING INTERSECTING PASSAGEWAYS WHEREBY ROTATION OF SAID SLEEVE WILL EFFECT LONGITUDINAL MOTION OF SAID PISTON TO THE POSITION WHERE THE PASSAGEWAYS INTERSECT, TORSIONAL SPRING MEANS CONNECTED TO SAID SLEEVE AND TO SAID CYLINDER AND ADAPTED TO BE STRESSED UPON ROTATION OF SAID SLEEVE, SAID TORSIONAL SPRING MEANS RETURNING SAID SLEEVE TO A PREDETERMINED POSITION UPON DEACTIVATION OF SAID ROTATING MEANS. 